Nickel catalysts are used in various connections in the chemical industry. The effective component is finely divided nickel, but different fields of application require different carriers for the catalyst metal. Within the field of hydrogenation of fats, or fat hardening, which is used for producing the raw materials for manufacturers of margarine, edible oils and the like, catalysts which contain nickel metal on a carrier of for example infusorial earth are used to a large extent. The carrier may possibly be mixed with or replaced by a synthetic material, for example a polymer. Since the finely divided nickel metal is pyrophoric, the catalyst is used suspended in solid or liquid fat. A usual kind of such a catalyst generally contains about 20-25% nickel, about 10-15% infusorial earth or the like and about 60-65% fat, preferably of vegetable origin.
After being used for some time, the catalyst is spent or "poisoned" as it is customary to say. This may be, for example, because the catalyst is mixed with inorganic or organic impurities from the reaction material. As a result, the catalyst becomes unsuitable for further industrial use. Since the nickel metal included in the catalyst represents a considerable value, a simple and cheap method of recovering nickel from spent catalysts of the type in question has long been sought.
In the German work "Forschung und Entwicklung zur Sicherung der Rohstoffversorgung", published by the Bundesministerium fur Forschung und Technologie, Bonn 1976, solutions hitherto proposed for recovering metal from this type of catalyst with a high content of organic components are given on page 90 et seq. It is stated that these solutions to the problem are based on calcining, grinding the residue from the calcining and wet chemical recovery of the metal. These methods are less suitable in practice, however, because during the calcining the catalyst carrier forms silicates or other compounds together with the metal, which compounds are very resistant to acids and therefore make the recovery of the metal more difficult and expensive. New methods of recovering catalyst metals for example nickel, are therefore being sought.